Line interface for combining a voice band signal and an XDSL signal on a twisted-pair copper line

A line interface for combining a broad-band XDSL signal and a voice-band telephone signal in a copper duplex cable, where the voice-band signal, over and above the voice signal, carries a DC feed for the user telephone and, during the call phase, also a ring signal. The XDSL signal and the voice signal are coupled to at least one primary winding of a line transformer of which the secondary winding pilots the telephone duplex cable. The secondary winding is not DC-coupled with the duplex cable and the ring and feed signals are injected into the duplex cable by a circuit realized in high-voltage technology and arranged in parallel with the secondary winding. A further inductive winding performs the function of compensating the flow variations induced in the core of the line transformer during the call phase.